Power source

ABSTRACT

A power system comprises a generator for generating electrical current, a rechargeable electrical storage device connectable to a load, and a source of non-electrical energy for driving the generator, the arrangement being such that energy output by the generator in excess of the power requirement of a load when connected to the battery is used to charge the battery.

The present invention concerns apparatus for generating electriccurrent. It is particularly concerned with providing a compact andreliable generator which is readily portable. Such a generator can findmany fields of application one of which would be for use in providingpower for portable radios, computers and other electronic equipment inenvironments where there is little or no provision of electrical mains.

It is of course well known to provide generators driven by peddle power.These require continuous effort in order to be operational. Additionallya radio having a removable spring-power generator has been disclosed inUK Patent Specification No 2262324. A more sophisticated form of amechanically powered generator is disclosed in European PatentSpecification No EP-A-96925832.6. As in the previous specification themain embodiment is applied to a portable radio.

The systems disclosed in these two patent specifications have a numberof disadvantages. Firstly when switched off the generator iselectronically braked. However this does not provide a full lock to thesystem and spring energy is slowly bled away through the system andlost.

A more important drawback is that a user of the system is unable tore-energise the spring, if this is the source of mechanical energy,whilst maintaining the requisite output current. Thus if the system isused in a radio and the spring winds down a user cannot re-energise thespring system and listen to the radio at the same time as winding thespring disengages any energy released to the generator and powerdelivery stops for the duration of the wind up.

Another disadvantage is that the energy capacity is limited to the sizeof the spring fitted. This provides for a limited play back period whenfully charged and should extended play times be required larger heavierand more expensive springs need to be fitted. Therefore relatively largeand expensive springs have to be used in order to provide acceptableplay times.

Finally, the spring, gear box, and generator combination specificallydisclosed in the above two specifications incurs quite heavy energylosses. The spring releases energy at a fixed rate equivalent to themaximum energy demanded by the radio, or any other load which may beapplied. Energy less than that is shunted and thus wasted. Thus thespring unwind duration is the same as the play time of the radio andtypically will be between 30 minutes and 1 hour. Frictional losses inthe transmission are roughly constant and are not dependent on theunwind velocity so that any attempt to increase unwind time has aconsequent energy penalty. From this it follows that the longer theunwind time of the spring the higher the energy content that is lostduring that unwind cycle.

International Patent Specification No. WO98/42060 discloses a portabletelephone set having a battery self-charging module having a manualdevice for driving a generator to charge a battery cell.

The present invention has as one concern to alleviate the abovementioned problems.

In accordance with the present invention there is provided a powersystem for supplying a variable load, the system comprising means formounting a rechargeable battery; a mechanical generator for generatingelectrical power; a source of mechanical energy for driving thegenerator, output terminal means for connection to a load, and a controlcircuit for controlling the supply of electric power to the outputterminal means, and wherein the mounting means and the generator areconnected in parallel to an output rail, whereby output energy of saidmechanical generator in excess of a load requirement is used to charge abattery mounted in said mounting means the output rail being connectableto said output terminal means by a mechanical switch which in its openposition prevents conduction through the rail and by a switchingtransistor located between the switch and an output terminal of theoutput terminal means, the arrangement being such that closure of theswitch enables a pulse to turn on the switching transistor to allowpassage of electrical current to the output terminal, maintenance of theswitching transistor in its on condition being dependent upon the outputvoltage supplied to the output terminal means being above apredetermined threshold.

In order that the present invention may be more readily understood anembodiment thereof will now be described by way of example and withreference to the accompanying drawings in which:

FIGS. 1A, 1B and 1C are perspective views of a radio which incorporatesthe present invention;

FIG. 2 is a circuit diagram of the radio receiver circuit of the radioof FIG. 1;

FIG. 3 is a circuit diagram of a power control circuit incorporated inthe radio of FIG. 1;

FIG. 4 is a circuit diagram of a second embodiment of a power controlcircuit incorporated in a radio receiver circuit which is substantiallythe same as the circuit of FIG. 2; and

FIG. 5 is an exploded view of the radio of FIG. 1.

Referring now to FIG. 1 of the accompanying drawings and in particularFIG. 1A it will be seen that the radio casing 1 has a loudspeaker grill2 and a pair of knobs 3 and 4 for controlling tuning and volumerespectively. A solar panel is shown at 5 and a folding aerial at 6.

The front end of the radio is semi-circular in side view and carries arotatable disc 7 in which is mounted a pivoted handle 8. As shown inFIG. 1A the handle is in its non-operative or retracted position but canbe swung out so that a user can rotate the disc using the handle so asto wind up a powerful spring mounted within the radio. The spring andthe bobbins on which it is mounted in the exploded view of FIG. 5. Aswill become apparent once the spring has been wound using the handle theenergy stored in the spring can be used to drive a generator to provideoperative current for a radio circuit shown in FIG. 2 of theaccompanying drawings.

The radio shown in the accompanying drawings can be powered in threedifferent ways, namely by spring power, from solar power generated bythe solar panel and from an external power source. An embodiment of acircuit for controlling these power sources will be describedhereinafter with reference to FIG. 3 of the drawings.

The radio circuit shown in FIG. 2 is essentially a custom made radioreceiver chip 200. A chip particularly suited for this purpose ismanufactured by Sony and is known as the Sony (RTM) CXA1691 radioreceiver chip. This chip includes all the aspects of a radio receiver,voltage regulator and an audio amplifier within a single chip.

In FIG. 2 the only variable external components to the chip 200 are anintermediate frequency transformer 10, FM and AM oscillators 11, 12, 13and antenna inputs 14.

In the present embodiment the FM coils are specified by the manufacturerbut by changing the AM RF coils the band over which the radio operatescan be changed from MW to SW1 to SW2 and LW.

As shown in FIG. 2 the radio circuit includes an earphone socket 15connected to an audio output line 16 and to a negative rail 17. Negativerail 17 is also shown as the negative output rail of the power controlcircuit shown in FIG. 3 and which is to be described hereinafter. Theearphone socket 15 is a switched socket so that when the input plug ofan earphone is inserted into socket 15 the previous connection to aloudspeaker 18 is broken and the audio output is taken to the nowconnected earphone. As can be seen loudspeaker 18 is also connected tothe negative rail 17 and to audio output line 16.

Also shown in FIG. 3 is a band select input line 19 which is connectedto the band select output of the power circuit of FIG. 3 and to apositive switched rail 20 which comprises the positive output from thepower circuit.

Turning now to the power control circuit shown in FIG. 3 it will be seenthat this also includes the positive supply rail 20 and the negativesupply rail 17 by means of which power is supplied to the radio circuit.

As already described this power control circuit is designed to controlthe supply of power to the radio chip circuit from three possiblesources, namely the solar panel 5, the generator shown at 25, a DCswitched socket 40 and a rechargeable battery 21.

The purpose of the power control circuit is to avoid the disadvantagesof prior circuits in which energy stored in a spring was released to agenerator in response to demand so that the unwind time of the springwas equivalent to the period over which the device could be used. In theembodiment being described the primary source of energy is the battery21 and the output of the generator 25 along with the output of the solarpanel 5 is used both to energise the radio receiver chip and to chargethe battery 21. Power from the generator 25 as it is driven by theunwinding spring enters the positive rail 20 via a Schottky diode 22which prevents any reverse current flowing back to the generator. In asimilar manner power from the solar panel 5 enters the positive rail 20via a second Schottky diode 23 which fulfils the same purpose as diode22.

When current is required for the radio chip this is switched on by meansof a three position switch 24 which also serves as a band select switchfor the radio circuitry, one of the switch outputs being the band selectline 19 shown in FIG. 2.

As well as being connectable to the radio circuitry via the switch 24the solar panel 5 and the generator 25 are connected to the battery 21so that the battery can take charge when the generator 25 is unwinding.As will be described in greater detail later the generator and solarpanel will normally preferentially charge the battery due to differencesin resistance between the battery and the load. Thus any excess powerwhich is generated by the generator 25 or the solar panel 5 which is notneeded for the function of the radio circuit is stored in the battery21. When the spring has unwound the power which has been stored in thebattery is then used to supply the radio circuit, along with power fromthe solar panel 5 if there is any ambient light.

When switch 24 is switched on to connect battery 21 to positive rail 20,and once the spring powered generator 25 has wound down it is necessaryto prevent battery 21 from completely discharging to 0 volts. This isachieved by the transistor switching circuit formed by transistors 26,27 and 28 and their associated resistors 29-36. Thus the circuitprovided by the transistors and resistors is essentially a low voltagecut-off circuit and in the present embodiment is arranged to isolate thebattery 21 from the radio circuit when the voltage of battery 21 fallsto below 1.8 volts. Thus using feedback transistors 26 and 27 switchtransistor 28 off when the battery voltage falls below 1.8 volts.Naturally this voltage level, which is a preferred level for Ni-Cadbatteries, can be adjusted by using other value resistors in theresistors 29-36 associated with the three transistors.

The capacitor 37 is included in the circuit to stop the “memory” typicalto Ni-Cad batteries from increasing the battery voltage in a transientfashion every time the radio circuit is disconnected by the transistorswitch circuit. Any increase over 1.8 volts would of course cause thetransistor switch circuit to reconnect the battery 21 to the radiocircuit. This would result in an oscillatory signal to the radio circuitwhich would in turn cause an unpleasant oscillatory sound from theloudspeaker.

As described when the radio is switched on the output from the solarpanel 5 is also used to drive the radio circuit and once again if thepower generated by the solar panel is in excess of the radiorequirements this excess power is stored in battery 21 for future useand also charges the battery when the radio is switched off.

The socket 40 shown in FIG. 3 is a switched socket 40 adapted toreceive, in the present embodiment, 4.5 volt input. Normally this DCvoltage would be generated by a mains adaptor (not shown). Entry of aplug from the adaptor or another power source into socket 40 disconnectsall battery charging, wind up and solar sections of the power controlcircuit so that the radio circuit is driven directly by the power inputto socket 40 without any charging of battery 21.

It is of course possible to arrange for the battery 21 to be charged bya voltage input to socket 40.

As already mentioned the power circuit described has a number ofadvantages over those arrangements in which power is taken directly fromthe. generator and lasts as long as the spring, or any other source, canprovide the necessary impulse to the generator.

The advantages of the power supply system described in particular withrespect to FIG. 3 and FIG. 4 is that batteries such as Ni-Cad batterieshave a high specific energy capacity. Thus small packages have arelatively high energy content. This allows relatively long play timesfrom a small product. Additionally as the power is effectively withdrawnfrom the battery rather than directly from the generator 25 power can bedrawn from the system at the same time as the mechanical power source isbeing replenished. Thus in the case of the radio disclosed in thisspecification, or in the case of a computer application the radio can beplayed and the computer used whilst the spring is being rewound. Ofcourse if the power source such as compressed gas was used to drive thegenerator a gas cylinder could be exchanged during play time withoutdeleterious effects. The same benefit would accrue if any type ofnon-electrical power source would readily be exchanged for a replenishedsource.

Another benefit from the system described in the specification is thatelectrical energy delivery by the battery to the load can be done at ahigh rate or a low rate at equal efficiencies. In effect the spring inthe present embodiment, or any other type of non-electrical power sourceacts as an energy buffer or an interim storage device between the humanoperator and the electrical generation system and the battery. Thisallows for a relatively large energy storage capacity in electricalform, that is the battery, but with only a relatively small springemployed. Additionally the generator and mechanical power sourcecharacteristics can be matched to the parameters of the battery and notof the load. Thus under most conditions energy can be released from thepower source to the battery at a steady pace uninfluenced by the demandsof the load and tailored to the most efficient transfer of energy fromthe non-electrical to the electrical state.

Where a spring is employed as the intermediate storage medium anotheradvantage is that all wind input rates are acceptable so that the systemcan be used by children and aged people as well as adults. In particularas the spring is not the main storage mechanism it may be relativelysmall and inexpensive. This allows for a very easy, low torque windcompared to the wind required when the spring is used as the mainstorage mechanism.

Finally because energy is released from the interior power source at aconstant and relatively low rate, and not at the energy input rate of ahuman being, a relatively small generator can be used which operates ata constant speed and allows for peak operating performance at designedparameters.

The embodiment of a power control circuit just described has adisadvantage that when turned off power leakage can occur via resistors29 and 30. The power control circuit shown at 100 in FIG. 4 is bothsimpler and avoids this problem. An added simplification, withconsequent reduction in cost, is provided by separating the channelswitching function from the control circuit. Thus FIG. 5 shows channelswitching by means of a switch 101 entirely separate from the controlcircuit 100. Other integers of FIG. 4 which are similar to those ofFIGS. 2 and 3 have been given the same reference numerals.

Turning now to the power control circuit 100 this is similar to thepower control circuit shown in FIG. 3 of the specification in that it isused to control the minimum discharge rate of a rechargeable nickelcadmium, nickel metal hydride or similar battery. These batteries do notnormally tolerate discharge below a minimum voltage, usually +/−0.8volts per cell.

The circuit 100 will connect power to the radio chip via a positive rail20 switched by a mechanical power switch 102 if the battery voltage isover the minimum allowed and will cut off when the voltage drops belowthe preset minimum. A single positive rail is used in this embodiment asthe rest of the circuitry is held at ground. When battery 21 is chargedand switch 102 is closed, a pulse will be created by the switchingaction and will pass a pulse of current through resistor 103 and acapacitor 104. The pulse will flow through diode 105 into the base of anNPN transistor 106. This causes transistor 106 to switch on “hard” andthus connect the base of a PNP transistor 107 to ground via a resistor108. Turning on transistor 107 causes current to flow to the radiocircuit and a voltage to be generated between the emitter of transistor107 and ground. The pulse will be short due to capacitor 104 blocking DCcurrent to the transistor 106 but resistors 109 and 110 form a voltagedivider which, if the battery voltage is high enough, will supply aconstant current to the base of transistor 107 to keep it turned on.

Thus the current being constantly supplied to the base of transistor 107is dependent on the battery voltage and the values chosen for resistors109 and 110. When the battery voltage drops below the threshold valueset by these two resistors the current to the base of transistor 107will no longer be enough to keep it on “hard” and so will not keep theconnection of the base of transistor 106 closely enough to ground tokeep switched on. As transistor 106 starts switching off the voltagebetween resistors 109 and 110 will drop as well thus lowering thecurrent to transistor 107 causing an avalanche effect until bothtransistors are completely off.

In this situation the battery 21 can be recharged while still connected,but without a trigger pulse to the base pin of transistor 106 the switchon process involving transistor 107 cannot start.

To trigger the transistor 106 a pulse can be provided in different ways.

If the generator 25 is started current will flow from the generator viaa diode 112, a resistor 111 and diode 105 to the base of transistor 106.This will switch on transistor 107 but only as long as the generator 25is functioning or the battery has a higher voltage than the thresholdswitch-off voltage. If the battery is flat and the generator is turnedon just momentarily, the output will switch on but after a short whilewill switch off again. In order to ensure this resistor 111 has arelatively high value so that it passes only just enough current topulse open the transistors 106, 107.

Alternatively if the solar panel is exposed to enough light current willflow through a diode 113, resistor 111 and diode 105 to the base oftransistor 106 once again switching on the transistors 106 and 107.Transistor 107 will remain switched on only as long as the solar panelis generating sufficient current or the battery has a higher voltagethan the threshold switch of voltage. Thus if the battery is flat andthe solar panel is exposed just momentarily to light the output willswitch on but after a short while will switch off again.

These alternative starting operations are important in dealing with thesituation where a user has left the radio on and all power has run downwithout switch 102 being opened and means that a user can restart theratio by charging the battery without having to first open and thenclose the switch 102.

To trigger transistor 106 without the help of generator 25 or solarpanel 5 as previously described, for example after a full charge of thebattery from an external charge connected to socket 114, it is necessaryto open switch 102 which will allow capacitor 104 to discharge viaresistors 103 and 115 so that when the switch is closed the closingaction can generate the necessary pulse to trigger the transistors 106and 107 into conduction.

In an environment where external power supplies are readily available tocharge the rechargeable battery it will be natural for a user to takeadvantage of this facility as the playtime of even a relatively smallbattery will be considerably in excess of the playtime available from aspring-powered generator unless the generator is unfeasibly large. Atypical battery capacity would require 360 to 500 milliamp hours tocharge completely and this is far beyond the capacity of aspring-powered generator of a reasonable size. Thus the battery capacityis of at least a magnitude greater than the generating capacity ofspring-powered generator 25. In the present embodiment thegenerator/spring arrangement can generate a maximum of about 100 joulesof energy. A typical rechargeable battery of a size suited to a compactradio or other device can store between 3000-4000 joules.

In an environment where there is no external recharge facility themechanical generator is of prime importance so that any improvements inoperating efficiency are valuable. Thus the following description ismore concerned with the situation where the battery is not fullycharged. It will be appreciated that rechargeable batteries of thenickel cadmium, nickel hydride type the resistance to charge offered bythe battery varies with the degree of charge of the battery, theresistance being substantially lower where the battery is uncharged.Thus if the radio is switched on with the battery fully charged and thegenerator spring fully wound up the energy released by the generatorwill be largely wasted.

However, if the charge of the battery is low its resistance will be lessthan that of the load and the generator will preferentially recharge thebattery. As this recharging is basically independent of the load beingdrawn the spring can drive the generator at its optimum rate thussubstantially reducing the mechanical losses which have already beenreferred to. Thus the arrangement of the battery and generator inparallel to the positive supply rail as shown in the circuits of

FIG. 3 and FIG. 4 is particularly beneficial when the system is usedwith a discharged battery as the spring will be able to unwind to drivethe generator at a rate essentially independent of the load with asubsequent reduction in mechanical losses. Whereas in previousclock-work powered devices such as those described in UK PatentSpecification No. 2262324 where the spring may be unwinding for abouthalf an hour in the present embodiment while the spring-poweredgenerator unwinds at an optimum rate the unwinding period can be under10 minutes but will provide a play period substantially in excess ofthis. For example the play time in the present embodiment using thespring generators is substantially the same as in the radio disclosed inEP-A-96925832.6 but this playtime is achieved with a spring which hasonly 4000 of the energy storage capacity of the earlier model.

Turning now to FIG. 5 of the accompanying drawings which shows anexploded view of the radio of FIG. 1.

In FIG. 5 of the accompanying drawings images of the radio which arecommon to the embodiment shown in FIG. 1 in the previous figures havebeen given the same reference numerals. In FIG. 4 the rotatable disc andits pivoted handle 8 are shown in greater detail. Thus the handle 8carries on a cylindrical stub 8′ a winder knob 41 which can rotate aboutthe stub when the disc is being wound. A semicircular winder cap 42 isfitted over one half of the disc 7.

Reference has already been made to the presence of a powerful springwithin the radio. This spring is shown in FIG. 4 at 46. Whilst shown asa single coil in the figure it normally extends between a torque bobbin45 and a storage bobbin 47. The torque bobbin 45 has an end cap 43 andthe storage bobbin 47 has an end cap 44 with the spring 46 beingconfined within the bobbins and their associated end caps. Torque bobbin45 has a central spindle which passes through an opening in its end capto engage the disc 7 so that when the disc is rotated by the handle 8the spring 46 can be wound up.

The torque bobbin 45 cooperates with a ratchet ring 52 suitably securedto an input gear 53 having a toothed outer rim which cooperates with apinion gear 54 secured to a secondary gear 55 the toothed perimeter ofwhich survives a second pinion gear 54′ secured to a drive pulley 56.Drive pulley 56 is connected via a flexible belt (not shown) to agenerator pulley 50 secured to the shaft of the generator 25. In thismanner power from the unwinding of spring 46 can be transmitted via thegear train to the generator 25.

The torque and storage bobbins and the various gears and pinions areeffectively mounted on a gear plate shown at 51.

Other components of the radio shown in FIG. 4 comprise a dial window 57through which a dial drum 48 can be viewed, the dial drum carryingindicia showing the station to which the radio is tuned. Finally 58shows a ferrite bar used for AM reception.

It will be appreciated that the foregoing description has concentratedon a power system in combination with a device which utilises the powergenerated by the power source. It is of course perfectly possible forthe power source, integers, namely the generator, the solar panel, thebattery and the intermediate non-electrical power source to be entirelyseparate from its intended load and may in fact be designed to be usedwith a plurality of different loads such as computers, printers, playstations and the like. It will also be appreciated that the basicconcept described is not dependent on the use of a solar panel and thatthis element may be omitted.

What is claimed is:
 1. A power system for supplying a variable load, thesystem comprising: means for mounting a rechargeable battery; amechanical generator for generating electrical power; a source ofmechanical energy for driving the generator, output rails (17, 20) forconnection to a load, and a control circuit for controlling the supplyof electric power to the output rails, and characterized in that themounting means and the generator are connected in parallel to one outputrail, whereby output energy of said mechanical generator in excess of aload requirement is used to charge a battery mounted in said mountingmeans, said one output rail being connectable to said output terminalmeans by a mechanical switch which in its open position preventsconduction through the rail and by a switching transistor locatedbetween the switch and an output terminal of the output terminal means,the arrangement being such that closure of the switch enables a pulse toturn on the switching transistor to allow passage of electrical currentto the output terminal, maintenance of the switching transistor in itson condition being dependent upon the output voltage supplied to theoutput terminal means being above a predetermined threshold.
 2. A systemaccording to claim 1, wherein closure of said switch enables a pulse ofcurrent to turn on the base of a second transistor an output of which isconnected to the switching transistor to turn the switching transistoron.
 3. A system according to claim 2, wherein a voltage divider acrossthe output of the battery and generator is connected to the base of theswitching transistor so as to set the threshold beneath which theswitching transistor will not conduct.
 4. A system according to claim 3,and including an output path leading from said generator to the base ofthe second transistor so that a pulse from said generator can cause thesecond transistor to turn the power switching transistor on.
 5. A systemaccording to claim 4, wherein said path includes a resistor the value ofwhich is such that any output from the generator is only sufficient toturn on the second transistor.
 6. A system according to claim 1, andincluding a solar panel (5) in parallel with the generator and thebattery mounting means.
 7. A system according to claim 6, wherein theoutputs of the generator and the solar panel are connected to thebattery mounting by respective diodes to prevent back current from thebattery and solar panel.
 8. A system according to claim 1, and includinga nickel-cadmium or nickel-hydride battery the capacity of which issubstantially greater than the amount of electrical energy which can begenerated by said generator and mechanical power source.
 9. A systemaccording to claim 8, wherein the capacity of the battery is between3000 and 4000 joules and the total energy capacity of the mechanicalpower source is between 80 and 120 joules.
 10. A system according toclaim 1, wherein the mechanical power source is a spring; and whereinthe power source mounted in a removable cassette which is removable fromthe system so that power can be withdrawn from the battery by a loadconnected to the battery in the absence of the power source.
 11. Asystem according to claim 1, and including a socket through whichelectrical power can be input from an external source; and wherein useof the socket causes the generator and the electrical power storagedevice to be disconnected from a load so that a load can be drivendirectly by power input through the socket; and wherein power from thesocket can be used to charge the battery when mounted.